1. Field of the Invention
The invention relates to a volume-selective magnetic resonance method for determining a spectrum or a spectroscopic image of a region of an object which is arranged in a steady, uniform magnetic field, a volume-selective pulse and gradient sequence being applied to the region of the object in order to generate magnetic resonance signals, which sequence comprises a 90.degree. excitation pulse followed by a first and a second 180.degree. pulse, a magnetic field gradient superposed on the steady field being applied during at least one of the pulses in order to obtain volume-selective resonance signals.
The invention also relates to the use of such a method.
The invention also relates to a magnetic resonance device for volume-selective magnetic resonance spectroscopy or spectroscopic imaging, comprising means for generating a steady, uniform magnetic field, transmitter means for transmitting RF electromagnetic pulses to an object arranged in the steady field, means for generating magnetic field gradients superposed on the steady field, and receiver and processing means for receiving and processing magnetic resonance signals generated in the object, which processing means comprise programmed means which are operative to apply pulse and gradient sequences to the object in order to generate volume-selective magnetic resonance signals, which sequences comprise a 90.degree. excitation pulse followed by a first and a second 180.degree. pulse, at least one of which is volume-selective.
2. DESCRIPTION OF THE PRIOR ART
A volume-selective magnetic resonance method of this kind is known from EP-A 0 106 226, which corresponds to U.S. Pat. No. 4,480,228. According to such a method, an object is exposed to a slice-selective 90.degree. pulse, i.e. an RF pulse in the presence of a magnetic field gradient superposed on the steady field, after which it is exposed to slice-selective 180.degree. pulses, the respective gradient directions thereof extending mutually perpendicular. A magnetic resonance signal is thus obtained from a region of the object. The so-called spin-echo resonance signal arising after the second 180.degree. pulse is observed in the absence of gradients and is subsequently subjected to a Fourier transformation so that a localized spectrum is obtained from the region of the object.
Even though inhomogeneities in the steady field are refocused by means of the known so-called spin-echo method, the known method has the drawback that neat refocusing is not obtained for mutually weakly coupled nuclei in a molecule of the object, the so-called J-coupling. For example, in order to make a doublet visible in a molecule in which a group is weakly coupled to a proton in the molecule, a specific choice of the echo time is necessary. In the case of more complex molecules with different Js, a large number of couplings exists and one coupling can be made visible by a specific choice of the echo time. An example of such a more complex molecule is glutamate.